LiPF6-Based Locally High-Concentration Electrolyte Extends the Calendar Life of Lithium-Ion Batteries

Abstract

Due to the solvation structure of the Solvent-Separated Ion Pairs (SSIPs) within commercial electrolytes, the negative electrode fails to receive effective protection, leading to a considerable decline of lithium-ion battery capacity during the calendar aging process. At present, the use of lithium bis(fluorosulfonyl)imide (LiFSI)-based locally high-concentration electrolytes is an effective way to solve this problem, but due to the high cost and corrosiveness to the current collector, it has not been commercially utilized. Herein, a lithium hexafluorophosphate (LiPF₆)-based local high-concentration electrolyte is devised to address the challenge of calendar aging under conditions of high State of Charge (SOC). In this electrolyte, the solvated structure dominated by Contact Ion Pairs (CIPs) and Aggregated Species (AGGs), resulting from the interaction between the electrolyte and solvent, promotes the formation of an inorganic-rich Solid Electrolyte Interphase (SEI) film on the negative electrode, providing effective protection. The 18650 cylinder battery, constructed with NCA₈₁₁/Graphite, retains an impressive 85.52% capacity even after 90 days of storage at 55 °C. This work offers a viable approach to addressing the storage challenges of commercial lithium-ion batteries.